Objective　To investigate the effects and molecule mechanisms of nucleophosmin (NPM) mutation gene on cell proliferation and apoptosis in mouse fibroblast NIH/3T3 cells. 　Methods　Eukaryotic expression vector pEGFP-C1-NPMc

+

was transfected into NIH3T3 cells by Lipofectamine

and the positive clones were screened by G418. Then the expression of NPM mutation gene and protein were analyzed by PCR and Western blot analysis respectively. To observe

the effect of NPM mutation on cell proliferation in vitro

MTT and colony formation assays were used. To evaluate the mechanisms of cell proliferation induced by NPM mutations

the cell cycle and apoptosis were detected by FCM

meanwhile

the cycle regulatory factor p21 was analyzed by RTPCR and the activity of Caspase-3 was detected. 　Results 　NIH3T3 cells stably expressing NPM mutation were established. The growth ability and the rate of plate colony formation of cells in experimental group were significantly higher than the control groups (P0.05). Methylcellulose colony formation assay showed that cells of all groups could not form a colony in the cell culture media. Compared with control groups

the percentage of cells in the phase of G

2

was decreased remarkably (P0.01) and that in the phase of S was increased significantly (P0.01)

and the expression of p21 mRNA was reduced notably (P0.05). The rate of apoptosis and the activity of Caspase-3 were decrease remarkably (P0.01) in experimental group. 　Conclusion　NPM mutation gene in NIH3T3 cells can induce cell proliferation and inhibit apoptosis.